APPARATUS FOR WASHING OF PULP

Abstract: An apparatus for treating pulp with a treatment liquid, comprising a vessel (1) with a cylindrical wall (2), an internal straining member (3) for drawing off liquid from the pulp, together with a number of distribution pipes (5) on the outside of the vessel for supplying treatment liquid into the vessel via a number of inlet connections (6). According to the invention, each distribution pipe (5) is formed by an annular profile (20) and an opposite part (21) of the cylinder wall (2), the profile being welded firmly directly to the cylinder wall, and the profile and the cylinder wall part enclosing between them a distribution duct (22). Furthermore, each inlet connection (6) has an opening (23) which extends through the cylinder wall part and connects the distribution duct to the interior of the vessel.

Description: Apparatus for washing of pulp The present invention relates to an apparatus for treating pulp of cellulose-containing fibrous material with a treatment liquid, which apparatus comprises a vertical vessel with a rotationally symmetrical wall, a straining member arranged in the vessel for drawing off liquid from the pulp, together with liquid supply members for supplying said treatment liquid into the vessel, which liquid supply members comprise a number of distribution pipes which are arranged concentrically on the outside of the vessel and a number of inlet connections which connect each distribution pipe to the vessel. The distribution pipes which have previously been used in apparatus of the type indicated have the form of rings which are mounted at a distance from the rotationally syitimetrical wall of the vessel, which wall is usually cylindrical. The ring pipes communicate with the interior of the vessel via inlet connections which each have an inlet pipe connecting piece and a pipe bend which are joined by means of a flange/bolt joint. It can be seen that such an arrangement, with ring pipes hanging outside the vessel, requires extensive work in manufacture and assembly, in which the inlet pipe connecting pieces must be guided into bores in the cylinder wall and welded firmly in the cylinder wall before or after said flange/bolt joint is or has been made. Fitting in and welding of the many different components is complicated. In order to produce circular ring pipes, they must be bent by means of a complicated induction technique which requires special equipment which is not usually present in the workshop in which the apparatus is manufactured. One of the greatest disadvantages, however, is that the ring pipes and the inlet connections, which comprise inlet pipe connecting pieces and pipe bends, must be trial-assembled in the workshop before delivery, whereupon the parts are disassembled and marked in order then to be delivered to the place of use where they are assembled again according to the markings made. This final assembly is followed by complicated and time-consuming work to insulate the washing apparatus as each individual ring pipe must be insulated and an insulation must be mounted against the cylinder wall to extend within the insulation of the ring pipe. Moreover, complicated insulating covers with eccentric clips have to be manufactured and mounted around the pipe bends and adjacent flange/bolt joints. Since the insulation of the ring pipes and the inlet connections is not adequate, the ring pipes have to be warmed with electric current in order to prevent the treatment liquid freezing. As a result of the fact that the ring pipes have circular cross-section, it is difficult to connect a pipe connecting piece at a tangential or otherwise inclined direction in relation to the ring pipes and so the pipe connecting piece is instead connected radially, the liquid being distributed into the ring pipe in both directions during operation and the risk arising that the liquid becomes stationary on the diametrically opposite side with the attendant risk that fibres accumulate and completely or partially block up the ring pipe. As a result of the fact that the inlet connections are situated above the respective ring pipe, the system cannot be drained of remaining liquid to the vessel as an interruption takes place in production. The aim of the present invention is to reduce considerably the abovementioned problems and also in many cases completely eliminate them and to produce a washing apparatus with functionally and constructionally improved liquid supply members for treatment liquids which are easier to manufacture and mount than previously used liquid supply members, which can be mounted permanently on the vessel already in the workshop before delivery, which make possible simplified insulation of the vessel and the liquid supply members, and which result in improved operating safety. The apparatus according to the invention is characterized essentially in that each distribution pipe is formed by an annular profile and an opposite part of the rotationally symmetrical wall, the profile being firmly welded directly on the rotationally symmetrical wall, and the profile and said wall part enclosing between them an endless, annular distribution duct, and in that each inlet connection has an opening which extends through said wall part and connects the distribution duct to the interior of the vessel. The invention is described in greater detail in the following with reference to the drawings. Figure 1 is a side view of a section of a pressure diffuser which is provided with liquid-supply members according to a known construction. Figure 2 is a cross-sectional view according to the line II-II in Figure 1. Figure 3 is a view which shows parts of two adjacent liquid supply members of a pressure diffuser according to Figure 1. Figure 4 is a side view of a section of a pressure diffuser which is provided with liquid supply members according to the present invention. Figure 5 is a cross-sectional view according to the line V-V in Figure 4. Figure 6 is a cross-sectional view according to the line VI-VI in Figure 5. Figure 7 is a cross-sectional view according to the line VII-VII in Figure 5. Figure 8 is a cross-sectional view like that according to Figure 7 but showing another embodiment of the inlet connection according to the invention. In Figure 1, a section of a washing apparatus of the pressure diffuser type for treating pulp of medium consistency 6-18% is shown diagrammatically. The washing apparatus has a sealed vertical vessel 1 with a rotationally symmetrical wall 2 which in the embodiment shown is cylindrical. The wall can have another shape, if so desired, for example conical. Such a washing apparatus of normal size has a cylindrical wall with a diameter which exceeds 1 m and which is usually around 2-3 m. The pulp flows from an upper inlet to a lower outlet (not shown) of the vessel 1. A straining member 3 is arranged concentrically within the vessel 1 for drawing off liquid from the pulp, which passes by the straining surfaces of the straining member 3, the drawn off liquid being removed from the vessel via one or more outlets (not shown) . Situated on the outside of the vessel are liquid supply members 4 for supplying a suitable treatment liquid to the pulp, which treatment liquid replaces or displaces a corresponding quantity of the liquid phase in the pulp through the straining member 3. These liquid supply members 4 comprise a number of annular distribution pipes 5 (for example 12) which are arranged concentrically outside and at a distance from the cylinder wall 2. Each distribution pipe 5 communicates with the interior of the vessel 1 via a number of inlet connections 6 which also serve as bearing and mounting elements for fixing the distribution pipes 5 to the cylinder wall 2. Each inlet connection 6 comprises a pipe bend 7 and a radially directed pipe connecting piece 8 which is received in a hole 9 in the cylinder wall 2 and is welded firmly to the cylinder wall 2. The pipe bend 7 and the pipe connecting piece 8 are rigidly connected to one another via a flange/bolt joint 10. A small sleeve 16 is welded firmly to the pipe bend 7 in order to form a straight cleaning opening into the pipe connecting piece 8 when a closure is removed from the sleeve 16. The pipe bend 7 and the flange/bolt joint 10 are enclosed by a detachable insulating cover 11. Treatment liquid is pumped into the distribution pipe 5 through a pipe connecting piece 17 which is directed radially in relation to the distribution pipe 5 so that the treatment liquid is distributed to the inlet connections 6 in both directions. 12 indicates an insulation which surrounds the distribution pipe 5 and 13 an insulation which surrounds the cylinder wall 2. Situated on the inside of the vessel 1 is a number of cylindrical screens 14 for internal distribution of the treatment liquid which flows in through each horizontal group of inlet connections 6 and then through the respective annular gap space 15 which is delimited by the screen 14. The embodiment of the liquid supply members 4, which has been described above and is shown in Figs 1-3, is that which has generally been used previously and which leads to a series of disadvantages as discussed in the introduction. In Figure 4, a section of a similar washing apparatus is shown diagrammatically, which apparatus is provided with liquid supply members 4 made according to the present invention. The washing apparatus itself has the same general construction as the washing apparatus shown according to Figure 1 and the same reference numbers are therefore used for equivalent or similar construction elements or for construction elements with the same function. In the cross-sectional view according to Figure 5, however, the straining member has been omitted for the sake of simplicity. The liquid supply members 4 for supplying treatment liquid comprise in this case also a number of distribution pipes 5 but these are, according to the present invention, constructed and arranged in a completely different manner. According to the invention, each distribution pipe 5 is thus formed by a radially inwardly open profile 20 and an opposite part 21 of the cylinder wall 2, the profile 20 being firmly welded directly on the cylinder wall 2 so that the profile 20 and the cylinder wall part 21 enclose between them an annular concentric distribution duct 22. The liquid supply members 4 also comprise a number of inlet connections 6 which, according to the present invention, have radial openings 23 which extend through the cylinder wall part 21 and connect the distribution duct 22 to the interior of the vessel 1 which comprises the vertical annular gap space 15 which is delimited by the screen 14. As the distribution pipe 5 bears tightly against the outside of the cylinder wall 2, any form of external pipe-laying is eliminated. In the simplest embodiment, each such opening is formed by a radial borehole which is made in the cylinder wall 21. This embodiment, however, can be used only in cases where the operating conditions are well known with regard to the actual production and the pressure conditions in the distribution duct and the interior of the vessel so that the correct dimension of the borehole can be selected from the very outset in order to make it possible for the same quantity of treatment liquid to be fed in per unit of time through all boreholes which lead out from one and the same distribution duct 22. If the borehole is intentionally or unintentionally given too great a diameter, the opening can comprise a throttling facility, for example by covering the borehole with a washer which has a central hole with a smaller diameter than the borehole. Such washers are easily exchangeable in order for it to be possible to adapt the throttling to the operating conditions, a selection thus being made from a stock of washers with varying diameters. In the embodiment shown in Figures 6 and 7, each opening 23 is formed by a central hole of a bushing 24 which is screwed into a threaded borehole 25 in the cylinder wall part 21. Like the washer described above, the bushing 24 can easily be exchanged for other bushings, the central holes 23 of which have different diameters so that an adaptation can be made to the prevailing operating condition and the same quantity of treatment liquid ultimately fed in per unit of time from the distribution duct through all bushings 24 having the same diameter of the central hole. In line with each opening 23, the outer vertical wall of the profile is provided with a sleeve 26 which can be sealed with a plug 27 which can be screwed into the sleeve. When the plug 27 is removed, the distribution duct 22 and the bushing 24 become accessible via the hole 28 of the sleeve 26 and a tool can also be introduced through the hole 28 in order to remove the inner bushing 24 and replace it with another. Via this sleeve 26, the distribution duct 22 and the opening 23 can also be cleaned of fibre accumulations if so required. Each distribution pipe 5 has an outer inlet pipe connecting piece 29 which is connected to a source of treatment liquid via a line (not shown) , the inlet pipe connecting piece being directed obliquely in towards the outer circumference of the profile 20 in a tangential or essentially tangential relationship, in which the actual chord which intersects the outer circle encloses a sector angle of from 0° (that is to say a tangential relationship) to around 50°. In the embodiment shown in Figure 5, this sector angle is around 47°. By arranging the inlet pipe connecting piece 29 obliquely in relation to the distribution pipe 5, the treatment liquid will flow through the distribution duct 22 in a single direction so that there are no places with stationary liquid and the risk of fibre accumulation is significantly reduced. It is preferred that the profile 20 has a rectangular cross-section as is shown in Figures 6 and 7. It can expediently be built directly on the cylinder wall by two plates being welded firmly in sections at right angles to the cylinder wall and at a predetermined distance from one another, after which a plate is welded firmly in sections to the outer edges of the two plates already anchored. The rectangular shape of the distribution pipe 5 is also advantageous for the reasons that it facilitates safe and firm welding of the inlet pipe connecting piece 29 at an oblique direction in relation to the plane outer plate, and also provides a good and symmetrical flow profile. It is preferred to arrange every other opening 23 in the lower part of the distribution duct 22 and every other opening 23 in the upper part of the distribution duct 22 as is shown in Figure 6 and Figure 7 respectively. Venting of the distribution duct 22 can thus take place during operation through the higher placed openings 23, and fibres can be removed more easily from the distribution duct during operation through the lower placed openings 23. The entire distribution duct 22 is thus accessible in every cross- section in order to receive and distribute the treatment liquid. In Figure 8, another embodiment of the inlet connection 6 is shown, in which the opening 23 comprises a throttling facility which is formed by a central hole 30 of an exchangeable throttling nut 31 which is screwed onto an outwardly threaded bushing 32 which is received in a borehole 33 in the cylinder wall part 21 and is firmly welded to this. This throttling nut 31 is easily exchangeable for a throttling nut with a different diameter of the central hole 30 via the hole 28 after removal of the plug 27. By designing the liquid supply members according to the present invention, a considerably lower manufacturing cost is achieved and the washing apparatus becomes more compact and thus less space- consuming as emerges from a comparison between Figures 1 and 4. The insulation 34 is simplified and the internal, protected positioning of the openings 23, that is to say in the cylinder wall part 21, means that the distribution duct 22 requires no electrical warming. The invention moreover makes it possible to simplify the construction of the top of the washing apparatus so that a previously used plastic hood can be replaced with a simple beam system and an insulating plate. A further advantage is that the lower placed openings 23 make it possible for most of the liquid in the distribution ducts 22 to be self-drained to the vessel when the washing apparatus is shut off in connection with service or other interruption in production.

Claims: PATENT CLAIMS 1. Apparatus for treating pulp of cellulose- containing fibrous material with a treatment liquid, which apparatus comprises a vertical vessel (1) with a rotationally symmetrical wall (2) , a straining member (3) arranged in the vessel (1) for drawing off liquid from the pulp, together with liquid supply members (4) for supplying said treatment liquid into the vessel (1) , which liquid supply members (4) comprise a number of distribution pipes (5) which are arranged concentrically on the outside of the vessel (1) and a number of inlet connections (6) which connect each distribution pipe (5) to the vessel (1) , c h a r a c t e r i z e d i n that each distribution pipe (5) is formed by an annular profile (20) and an opposite part (21) of the rotationally symmetrical wall (2) , the profile (20) being firmly welded directly on the rotationally symmetrical wall (2) , and the profile (20) and said wall part (21) enclosing between them an endless, annular distribution duct (22) , and in that each inlet connection (6) has an opening (23) which extends through said wall part (21) and connects the distribution duct (22) to the interior of the vessel. 2. Apparatus according to Claim 1, c h a r a c t e r i z e d i n that the profile (20) has a rectangular cross-section. 3. Apparatus according to Claim 1 or 2, c h a r a c t e r i z e d i n that the inlet connection (6) comprises a bushing (24) , the central hole of which forms said opening (23) . 4. Apparatus according to Claim 3, c h a r a c t e r i z e d i n that the bushing (24) can be exchanged for a bushing with a different diameter of the central hole (23) . 5. Apparatus according to Claim 1 or 2, c h a r a c t e r i z e d i n that the opening (23) comprises a throttling facility (30) . 6. Apparatus according to Claim 5, c h a r a c t e r i z e d i n that the inlet connection (6) comprises a firmly arranged bushing (32) and in that said throttling facility is formed by a throttling nut (31) which is borne by the bushing (32) , said opening (23) being formed by the central holes of the bushing (32) and of the throttling nut (31) , which are coaxial with one another. 7. Apparatus according to Claim 6, c h a r a c t e r i z e d i n that the throttling nut (31) can be exchanged for a throttling nut (31) with a different diameter of the central hole (30) . 8. Apparatus according to any one of Claims 1-7, c h a r a c t e r i z e d i n that the liquid supply member (4) comprises an inlet pipe connecting piece (29) which is firmly connected to the distribution pipe (5) at an oblique direction in relation to the distribution pipe in its plane. 9. Apparatus according to any one of Claims 1-8, c h a r a c t e r i z e d i n that a first group of openings (23) , preferably every other opening (23) , is arranged in the lower part of the distribution duct (22) , and a second group of openings (23) , preferably every other opening (23) , is arranged in the upper part of the distribution duct (22) .

Inventors: NILSSON MIKAEL, WILKE BO, NILSSON, MIKAEL, WILKE, BO
Applicants: KVAERNER PULPING TECH, NILSSON MIKAEL, WILKE BO, KVAERNER PULPING TECHNOLOGIES AB, NILSSON, MIKAEL, WILKE, BO
Application year: 1994
Main classification: D21C9
IPC codes: D21C9, D21D1, D21D5